Chronic infection with Chlamydia pneumoniae (CP) is associated with development of coronary disease. However, little information exists concerning CP infection and impact on posttransplant cardiac allograft vasculopathy (CAV). A total of 202 patients were investigated 5.5+/-3.1 years after cardiac transplantation (46.5+/-11.0 years; 169 male, 33 female). Assessment of CAV was performed by annual coronary angiograms. Chlamydia serology (IgG/IgA) was performed using micro-immunofluorescence. Statistics comprised analysis of variance and Kaplan-Meier analysis. A total of 152 patients were CAV positive. Elevated titers were present in 45% (IgG) and 72.8% (IgA) of patients. Generally, serostatus was not associated with development of CAV when evaluated over the total postoperative interval. However, after month 14 there was a significant trend toward lower actuarial freedom from CAV in patients with elevated IgA titers. CP seems not to play a significant role in the development of CAV early after heart transplantation but might be a predicting risk factor after the first postoperative year.